Alaska Extended Forecast Discussion National Weather Service College Park MD 712 PM EDT Sun May 25 2025 Valid 12Z Thu 29 May 2025 - 12Z Mon 02 Jun 2025 ...General Overview... Much of mainland Alaska will generally be sandwiched between two upper-level gyres during much of the medium-range period. One gyre rotating over the Arctic Ocean will send disturbances toward the North Slope while the other gyre will continue to send disturbances from the Bering Sea and North Pacific eastward toward the Gulf of Alaska and the Alaska Panhandle. By late this week, there is decent model agreement for a negatively-tilted upper ridge to establish over mainland Alaska as a fairly well-defined cyclone makes its way into the Aleutians by early next week. ...Guidance Evaluation and Preferences... With the presence of numerous smaller scale disturbances embedded within the aforementioned two upper-level gyres, the predictability of individual disturbances beyond Day 5 remains lower than normal. The largest model uncertainty today appears to be from the Bering Sea southward through the Aleutians from this coming weekend into early next week when a piece of upper low that breaks off from the Arctic gyre is forecast to dip south into the Bering Sea and interact with the next North Pacific cyclone moving into the Aleutians. The 06Z GFS and 12Z GFS are the northern and southern extremes on the spread of the cyclone track coming into the Aleutians while the 12Z ECMWF adopts a track in the middle of the GFS model spread late in the forecast period. The 12Z ECMWF track agrees very well with the consensus of the cyclone position by the 06Z GEFS, 00Z EC and 12Z CMC ensemble means. Over mainland Alaska, model guidance continues to show decent agreement for a negatively-tilted upper ridge to establish late this week and remain in place through the weekend into early next week. Meanwhile, models are in excellent agreement for the cyclone over the Gulf of Alaska to gradually weaken with time as it is forecast to edge closer to the Panhandle and the southern coastline of mainland Alaska. The WPC forecast package today is based on the consensus of the 12Z ECMWF/00Z & 12Z EC mean (40%), 12Z GFS/06Z & 12Z GEFS (40%), and 12Z CMC/CMC mean (20%) with ensemble means comprising the vast majority toward the end of the forecast period. WPC continuity is well-maintained. ...Weather/Hazards Highlights... Periods of rain and high mountain snow are expected from the Alaska/Kenai Peninsulas to the southeast Panhandle region, with the greatest coverage and intensity expected from Juneau and points south, where heavy rain appears most likely as the medium- range period begins on Thursday before gradually tapering off later that day. Farther inland across the interior section of mainland Alaska, scattered afternoon and evening thunderstorms are likely to develop from the southwestern interior through eastern interior sections in the presence of an unstable airmass. There is a tendency for these activities to expand toward northeastern Alaska by late this week as southerly flow begins to establish under the above-mentioned upper-level ridge. Lightning strikes from these storms may increase the threat of wildfires in the region. Across the North Slope, it will be cold enough for occasional wet snow to fall especially toward the high elevations of the Brooks Range midweek when a frontal wave lingers just to the south. The snow should become more scattered and shorter in duration by late this week. Temperatures overall are expected to be near to slightly above average for late May standards across the central and southern mainland but slightly below normal north of the Brooks Range. Cooler conditions are also likely for the coastal areas and the near shore islands due to increased cloud cover and rainfall. Meanwhile, a slow warming trend is forecast for the entire Alaskan domain as upper ridging is predicted to set in when June will be around the corner. Kong Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html